Recent studies have revealed that substantial quantities of per- and polyfluoroalkyl substances (PFAS) are retained in source zone soil, which suggests that PFAS release from soils to groundwater is a rate-limited process. Yet the understanding of the fate and transport of PFAS remains limited, as the current knowledge is derived from adsorption/desorption studies mainly focused on the effects of physicochemical properties such as pH, organic matter, and other soil characteristics on PFAS retention and release. However, in the natural environment, most soil/sediment particles are also colonized by microorganisms that commonly grow in aggregate in extracellular polymeric matrices, known as biofilms. Two recent studies have observed bioaccumulation and retention of PFAS in natural biofilms. Similarly, many microorganisms in the environment produce natural biosurfactants. These compounds may play a critical role in enhancing the desorption of PFAS, particularly in aqueous film-forming foam (AFFF) source areas. The role of biofilms and biosurfactants on PFAS fate and transport is poorly understood. Accordingly, the goal of this proof-of-concept project is to determine the extent to which biofilms (and their associated bacteria) and biosurfactants may impact rate-limiting processes that control PFAS retention/release and transport in soils.

The overarching hypotheses of this research project are i) that biofilms can dramatically influence sorption of PFAS in porous media; and ii) that biosurfactants can mobilize PFAS and promote their transport through porous media. The overall technical objectives will address the following questions:

• Will PFAS in pore water or bulk solution be sorbed to biofilms at the surface of a solid matrix?
• Do biofilms produced by different bacterial strains promote differential sorption of PFAS?
• Will the presence of biosurfactants lead to desorption and enhanced transport of PFAS through soil?
• How do biosurfactant effects vary with respect to the PFAS properties (e.g., carbon chain length, functional groups, and charges)?

These questions will be addressed through two primary tasks, using both batch and column studies: Task 1: Role of Biofilms and Bacterial Cells in PFAS Sorption and Task 2: Effects of Biosurfactants on PFAS Desorption and Transport.

This project is designed to examine the unexplored and not well-understood aspects of biofilm-coated soils, and the presence and absence of biosurfactants, on the fate and transport of PFAS. A better understanding of the fate and transport of PFAS in the subsurface will provide critical information for developing effective strategies for managing numerous PFAS-impacted sites, which will ultimately improve the efficiency of cost-effective, field-ready solutions for PFAS treatment, ensuring DoD installations remain mission-capable while safeguarding critical defense infrastructure and the workforce. (Anticipated Completion Date - 2026)